The myogenic response is an intrinsic contraction in response to elevated intravascular pressure. It is most pronounced in arterioles and it establishes a basal constriction upon which other control mechanisms cause vasodilation or vasoconstriction. This project will examine signaling pathways linked to a mechanosensitive cation channel in arteriolar smooth muscle that is activated by longitudinal, whole-cell stretch. The central hypothesis to be tested is that the mechanosensitive channel plays a primary role in the initial signaling events leading to a myogenic contraction. The interaction of this channel with other ion channels, the cytoskeleton, and with protein kinases determines the sensitivity of vascular smooth muscle to stretch. The investigations will use whole-cell patch clamp, fura-2 microflourimetry, and analysis of protein phosphorylation on arteries and arterioles from pig coronary vasculature. There are 3 specific aims: The first aim will determine which ion channels are activated "down stream" from the mechanosensitive channel; the hypothesis being that stretch will open mechanosensitive channels that will depolarize the membrane causing activation of Ca channels. The increased calcium will then partially inactivate the mechanosensitive channel and also activate the Ca-activated potassium channels causing repolarization. The second aim will determine how the sensitivity of the mechanosensitive channel is modulated by protein kinase dependent phosphorylation; the hypothesis being that phosphorylation of the channel by protein kinase A and C will enhance the mechanosensitive channel response to stretch. The third aim will determine the mechanisms by which integrin-mediated signaling pathways modulate ion channel function and myogenic response; the hypothesis being that ligation of the alpha-v-beta-3 integrin receptor modulates the sensitivity of both calcium channels and mechanosensitive channels, that tyrosine phosphorylation of voltage gated Ca channels, mechanosensitive channels, and possible cytoskeleton is required for normal myogenic response.